Process for the electro-plating of cadmium-titanium alloy



United States Patent Ofiice 3,083,150 PROCESS FOR THE ELECTRG-PLATING OF CADMIUM-TITANIUM ALLOY Koji Takada, Shinjuku-ku, Tokyo, Japan, assignor to Toyo Kinzokukagaku Kabushikikaisha, Tokyo, Japan No Drawing. Filed Mar. 6, 1961, Ser. No. 93,356 Claims priority, application Japan Feb. 7, 1961 4 Claims. (Cl. 20443) This invention relates to a process for the electroplating of cadmium-titanium alloy, wherein a titanium compound is dissolved in a cadmium cyanide plating bath and the solution is subjected to electrolysis, using a conventional cadmium as anode, in order to obtain an anticorrosive coating consisting of an alloy of cadmium with titanium.

Generally speaking, to obtain the electro-deposition of titanium from its aqueous solution is thought to be impossible, because of the low electrode potential of titanium.

Even by electrolysis of the aqueous solutions of titanium salts with an insoluble anode or titanium anode, the electro-deposition of metallic titanium is not observed. More specifically, for instance, titanium salts, namely, titanium sulfate, chloride, fluoride, oxalate, citrate, tartrate, etc. are soluble in neutral or acidic aqueous solutions, but are insoluble in alkaline aqueous solutions producing quite a precipitate of titanium hydroxide by hydrolysis reaction.

When various kinds of titanium salts and cadmium salts, namely cadmium sulfate or fluoborate, are added to a neutral or an acidic solution and the electrolysis is carried into effect, metallic titanium will not deposit on the cathodic electrode surface at all, resulting only in coating a cadmium layer.

This is explained by different galvanizing potentials between titanium and cadmium. The same phenomenon is observed in electrolysis of solutions that contain copper sulfate and zinc sulfate; electro-plating of brass will not be obtained.

In the case of titanium, however, titanium salts are easily decomposed in alkaline aqueous solutions and become the precipitation of titanium hydroxide, so that usual titanium salts cannot be added to an alkaline plating bath like a cadmium cyanide bath. It is, therefore, the main object of the present invention to provide a novel electro-plating process to produce more efiicient and superior anti-corrosive coatings in an economical and industrial manner than conventional cadmium coating methods. Another object of the invention is to provide a novel electro-plating process, in which coatings consisting of cadmium-titanium alloy may be produced in an amazingly effective manner.

A further object of the invention is to provide a novel electro-plating process to obtain plating coatings of relatively higher surface-hardness than conventional cadmium platings.

Other objects and advantages of the invention will be apparent from the following description.

This invention is the method in which cadmiumtitanium alloy plating is obtained by electrolysis of a cadmium cyanide plating bath being gradually added to a special titanium compound.

In the case of the plating according to this method, conventional cadmium metal is used as anode and titanium is dissolved in the plating bath as sodium pertitanate. In practice, it is preferred that a continuously operating filter be connected to the galvanizing vessel and the filter charged with the titanium compound, the additional reaction product of tetravalent titanium hydroxide with hydrogen peroxide. In the course of the process, the

Patented Mar. 26, 1963 galvanizing bath is continuously circulated through the filter, thereby dissolving the titanium compound in the solution to a saturated concentration. By this procedure, the concentration of the sodium pertitanate can always be kept at a constant value during the plating.

Sodium pertitanate is a stable in an alkaline cadmium cyanide plating solution of pH-values 13-14, and does not tend to precipitate by hydrolysis in the solution or to be reduced to a metallic state by hydrogen activated by cadmium with high hydrogen over voltage on the cathode. Thereafter, it easily alloys cadmium of the packed hexagonal system, crystalline structure. This fact is determined by the Mattauchs mass-spectrum analysis. The thus obtained cadmium-titanium alloy coating shows a higher anti-corrosive quality several times as strong as a conventional cadmium plating, determined by a number of tests using salt spray and by exposure tests, There are apparently considerable differences in electron microscopic structure between cadmium-titanium alloy coating and conventional cadmium alloy coating.

It has been found according to this invention, that by adding a small amount of titanium to the coating layer, the physical and chemical properties of the coating are substantially improved in comparison with conventional cadmium plating.

The plated surface according to this method is not only excellent in anti-corrosive and uniform qualities, but also has a satisfactory mechanical workability after being plated for pressing, deep-drawing, and bending, in addition to a comparatively higher hardness than a conventional cadmium plating.

This plating may be carried into effect with a current density of 2-5 amperes per square decimeter with a high throwing power. In the rotary barrel plating, the process may be carried into effect with use of a current density of l-3 amperes per square decimeter, with equal results.

The invention will now be described more in detail, referring to a preferred numeral example.

Example To a cadmium plating bath, containing 30 grams of cadmium cyanide, 50 grams of sodium cyanide and 20 grams of caustic soda per litre of solution, is continuously added the titanium compound obtained by the additional reaction of orthotitanic acid with hydrogen peroxide so as to maintain the concentration at a rate each of 0.5-1 gram per litre of liquid, in such a way that the liquid is continuously passed through a filter charged with the said compound. The galvanization is carried into effect, using a conventional cadmium plate as anode, with a cathodic current density of 4 amperes per square decimeter for 15 minutes, thus obtaining a uniform, bright, superior and well-deposited layer of cadmium-titanium alloy.

The thus coated layer is 20 microns in thickness and contains about 0.3% of titanium as determined by the spectrum analysis, and perfectly certified by the Mattauchs mass analysis that titanium in the layer remains in a metallic state.

It will be clear from the foregoing, the invention, cadmium-titanium alloy coatings may be produced by a simple technique and with substantially more effective and superior anti-corrosive characteristics than those obtainable by conventional cadmium plating. The process according to this invention represents a highly advantageous galvanizing method, which is easily carried into practice in an economical and industrial manner.

Although a preferred example of the invention has herein been disclosed for purpose of illustration, various modifications thereof, after study of this specification,

that according to Letters Patent is:

30 grams of cadmium cyanide 50 grams of an alkali metal cyanide 0.5-1 gram of sodium pertitanate sufiicient quantity of alkali to maintain a pH of between 2. An aqueous electrolytic bath for electroplating an alloy consisting of cadmium and titanium employing a cadmium anode containing the following compounds in grams per liter of water:

30 grams of cadmium cyanide 50 grams of sodium cyanide 20 grams of sodium hydroxide 0.5-1 gram of sodium pertitanate.

.3. A method for electroplating an alloy consisting of cadmium and titanium comprising utilizing a cadmium anode, employing an aqueous electrolytic bath containing the following compounds in grams per liter of Water:

grams of cadmium cyanide grams of an alkali metal cyanide 0.5-1 gram of sodium pertitanate sutiicient quantity of alkali to maintain a pH of between and current density of 1-3 amperes per square decimeter.

4. A method for electroplating an alloy consisting of cadmium and titanium comprising utilizing a cadmium anode, employing an aqueous electrolytic bath containing the following compounds in grams per liter of water:

30 grams of cadmium cyanide 50 grams of sodium cyanide 20 grams of sodium hydroxide 0.5-1 gram of sodium pertitanate and current density of 1-3 amperes per square decimeter.

References Cited in the tile of this patent UNITED STATES PATENTS 2,646,397 Wean July 21, 1953 FOREIGN PATENTS 762,199 Great Britain Jan. 20, 1954 1,215,884 France Nov. 23, 1959 

1. AN AQUEOUS ELECTROLYTIC BATH FOR ELECTROPLATING AN ALLOY CONSISTING OF CADMIUM AND TITANIUM EMPLOYING A CADMIUM ANODE CONTAINING THE FOLLOWING COMPOUNDS IN GRAMS PER LITER OF WATER: 30 GRAMS OF CADMIUM CYANIDE 50 GRAMS OF AN ALKALI METAL CYANIDE 0.5-1 GRAM OF SODIUM PERTITANATE SUFFICIENT QUANTITY OF ALKALI TO MAINTAIN A PH OF BETWEEN 13-14. 